Although all men differ in natural strength, they are all fundamentally equal in their ability to physically harm or kill another by various means. While fear may dissuade them temporarily, if two people ever desire the same thing, the natural consequence is war. Due to this selfish nature, he is unable to live in peace with others. He will always do whatever it takes to move ahead, simply because it is advantageous to him at that time. It is for this reason that a social contract is necessary, with a sovereign power to keep him in check. In Hobbes’ Leviathan, he outlines what this social contract is, why it is crucial for men to have, and what mutual obligations transpire.
A contract is a covenant made where one or more parties are bound to some future obligation, whether it be for a trade of services or a transfer of rights. A basic social contract must have vested power in one central, sovereign authority, with power to punish those who break the contract. Under the rule of the sovereign, men are impelled, by fear, to keep the contract intact. Without the fear of punishment for breaking contracts, men will break them whenever it is immediately advantageous for them to do so. It should be noted that Hobbes believes a covenant is only valid if a common power can enforce the terms of the contract. If two people simply agree not to attack one another without something to enforce this they have no reason to obey the covenant. One might argue that the desire for peace could be enough to enforce the terms of the contract, but in this case, the desire to cheat and, say, attack the other person once their guard is down would be too tempting. In fact, not only would it be tempting, it would also be the most rational course of action.
A social contract is necessary because of man’s state of nature, which Hobbes' portrayal of is purely descriptive rather than normative. That is to say, Hobbes’ does not believe there is anything necessarily wrong with the passions and desires that propel men towards war with one another. In fact, in a state of nature where there is no common power, "nothing can be unjust. The notions of right and wrong, justice and injustice have there no place. Where there is no common power, there is no law; where no law, no injustice."(742) The terms of peace that men come into agreement upon, which are dictated to us by reason, are called the Laws of Nature. To fully understand these Laws one must first understand the fundamental right of nature these are based upon. The right of nature is the liberty each person has to do anything within their means for self-preservation. Correspondingly, a law of nature is a rule, discovered by reason that forbids one to do anything to hurt oneself, or to take away the means of self-preservation. The first fundamental law of nature, is that man should “seek Peace, and follow it."(743) The second fundamental law of nature derives from this first one, and states that we should lay down this absolute right of nature "and be contented with so much liberty against other men, as he would allow other men against himself."(743) In other words, men should restrain themselves from pursuing ends by any means necessary, insofar as others agree to do the same. The third law of nature proclaims that though the making of contracts is a necessary precondition to peace, men are obligated not only to make contracts but also to follow them.